Following high densification of a recording medium, wavelength shortening of a laser employed for reading/writing progresses from conventional red to blue. A nitride-based compound semiconductor, particularly a GaN (gallium nitride)-based material is employed for a blue laser. On the other hand, a VCSEL-based surface emitting laser structure observed in a red laser requires several 10 layers of reflecting mirrors (DBR) due to small refractive index difference of the same type of material in a GaN-based material. Therefore, it is difficult to prepare a VCSEL (Vertical Cavity Surface Emitting LASER)-based surface emitting laser, and only an edge emitting type laser is available. However, the performance of the edge emitting laser cannot be inspected before a cavity mirror is prepared by cleavage. Consequently, there arise such problems that a substrate cannot be effectively used while the yield is inferior, and the cost is increased.
While engineering development of the VCSEL-based surface emitting laser is also in progress, on the other hand, a photonic crystal laser is being noted as a novel laser against this. A photonic crystal is prepared by artificially forming a periodic structure of a dielectric. The periodic structure is formed by periodically providing a region different in refractive index from the dielectric body in the body. Bragg diffraction occurs in the crystal due to the periodic structure, and an energy band gap is formed in relation to the energy of light thereof.
Japanese Patent Laying-Open No. 2005-277219 (Patent Document 1) describes a photonic crystal laser employing a GaAs-based material as such a photonic crystal laser. In Patent Document 1, a material transmitting a laser beam is employed as an electrode material, to extract the laser beam by transmitting the same. However, a current must be increased in order to obtain high output, and the film thickness of the electrode must also be increased in order to increase the current. Although the electrode transmits the laser beam, absorption increases if the film thickness thereof is increased, and it is difficult to efficiently increase the output.
As other photonic crystal lasers, Japanese Patent Laying-Open No. 2003-273453 (Patent Document 2) and Japanese Patent Laying-Open No. 2004-253811 (Patent Document 3) describe lasers employing photonic crystals. In each of the photonic crystal lasers according to Patent Documents 2 and 3, no photonic crystal structure is formed immediately under an electrode but a photonic crystal structure is formed on another portion, to cause lasing by resonance. However, each of the photonic crystal lasers according to Patent Documents 2 and 3 employs no region into which carriers are sufficiently injected for the lasing and output improvement after the lasing, and hence it is disadvantageously difficult to obtain efficient output.    Patent Document 1: Japanese Patent Laying-Open No. 2005-277219    Patent Document 2: Japanese Patent Laying-Open No. 2003-273453    Patent Document 3: Japanese Patent Laying-Open No. 2004-253811